I. Field of the Invention
This invention generally relates to an X-ray diagnostic apparatus in which a transmitted X-ray image of an object under examination, e.g., a patient, is available for diagnostic purposes, and more particularly, to an X-ray diagnostic apparatus by which visible X-ray images of the object can be obtained, based only upon primary X-rays, without any adverse influences caused by the scattered X-rays.
II. Background Information
Generally, in the X-ray diagnostic apparatus set forth in the preamble, X-rays incident on an X-ray detector through the object under examination such as a patient contain not only primary X-rays but also X-rays which have been scattered by the object. The scattered X-rays constitute one of the major causes of deteriorated contrast and resolution in the transmitted X-ray image. This makes it necessary to eliminate the scattered X-ray components from the transmitted X-ray image data as provided by the X-ray detector.
One of the approaches to eliminate the scattered X-ray components is to use a so-called "Buckey Blade" or an elimination grid for the scattered X-rays (referred to as a "grid"). This approach involves a new problem in that there is a limit in the scattered X-ray elimination, because the grid per se produces the scattered X-rays incident thereupon.
The elimination of the scattered X-rays is very significant in the field of the X-ray diagnosis for the reasons that it improves an X-ray image quality, such as contrast and resolution, and thus allows a logarithm conversion of primary X-rays image data, thereby obtaining an accurate attenuation quantity of X-rays caused by the object when the X-rays pass through the object. Many studies have been made on the scattered X-rays, aiming at their effective elimination. The complicated phenomena of the scattered X-rays impede or almost reject a theoretical approach to this theme.
U.S. Pat. No. 4,549,307 reports a technique which establishes a total scatter radiation signal and then subtracts the total scatter radiation signal from the detected radiation signal. The scatter radiation signal is established by shielding portions of the detector and measuring radiation at the shielded portions of the detector to obtain a partial scatter radiation signal. The total scatter radiation signal is then reported to be interpolated from spatial distribution of the partial scatter radiation signal measured at the shielded areas.